1
Q
State the combined gas law.
A
PV = nRT
The product of pressure and volume is proportional to the absolute temperature.
2
Q
Demonstrate the working going from the combined gas law to the universal gas law.
A
PV/T = Constant (R)
Constant is proportional to the no. of moles of gas:
PV/T = nR
Rearrange the equation to get universal gas equation:
PV = nRT
3
Q
What is the molar gas constant?
A
8.31 J/K/mol
4
Q
Define:
diffusion
A
Movement of a substance from an area of high concentration to an area of lower concentration.
5
Q
What is the difference between diffusion and flow?
A
Flow is the bulk movement of fluid driven by pressure differences.
Diffusion is the passive, random movement of molecules resulting in net transport from high to low concentration.
6
Q
State Fick’s Law of Diffusion.
A
States that the rate of transfer of a gas through the membrane is:
- Proportional to tissue area
- Proportional to difference in gas partial pressure between two sides
- Inversely proportional to tissue thickness
7
Q
State the equation for velocity of diffusion across a membrane.
A
This is Fick’s law multiplied by a diffusion constant.
8
Q
State Graham’s law of diffusion.
A
Rates at which gases diffuse are inversely proportional to the square root of their densities.
9
Q
Which two factors affect the diffusion constant of a gas in a liquid?
A
- Solubility
- Molecular Mass (Square Root)
10
Q
What is the thickness of the respiratory membrane in a normal healthy lung?
A
0.5-1.0 µm
11
Q
What is the transit time for a red blood cell to pass through a pulmonary capillary?
A
0.75 s
NOTE: CO2 diffusion is complete in 0.10 s and O2 diffusion is complete in 0.30-0.40 s.
12
Q
State the steps to derive the equation for lung diffusion capacity.
A
Diffusion capacity incorporates the structural factors that affect diffusion (i.e. diffusion coefficient, area and thickness).
Based on the Fick equation:
Rate is proportional to (Diffusion Constant x Area x Partial Pressure Gradient)/Thickness
It is accounting for the three factors aside from partial pressure gradient.
13
Q
Why is carbon monoxide a useful agent for measuring the diffusion capacity of the lung?
A
- CO has similar diffusion properties to oxygen.
- CO is safe in small amounts.
- CO partial pressure in plasma is basically zero (i.e. P2 is zero).
- Negligible blood levels of CO at baseline.
14
Q
How is the diffusion capacity of the lung measured using the carbon monoxide breath hold method?
A
DLCO quantifies how much CO is transferred from the alveoli into the blood per minute per mmHg of mean alveolar CO partial pressure.
The patient inhales a gas mix containing ~0.3% CO and 10% helium to total lung capacity, holds their breath for 10 seconds, then exhales.
Helium dilution is used to estimate alveolar volume, while the fall in CO over time is used to calculate CO uptake (V̇CO).
Mean alveolar CO pressure (P̄ACO) is estimated from the remaining CO concentration, and:
DLCO = V̇CO / P̄ACO
15
Q
Define:
osmosis
A
Diffusion of a solvent across a membrane whilst the solute remains.
Quantified in terms of osmotic pressure which is the pressure required to stop the flow from one side of the membrane to the other.
16
Q
Define:
solubility
A
The amount (in moles) of a solute that can be dissolved in a unit volume of solvent under specified conditions.
17
Q
Define:
Henry’s law
A
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
18
Q
Describe how temperature affects the solubility of a gas in a liquid.
A
Solubility decreases.
Molecules gain kinetic energy as temperature rises, making it easier for it to escape from the liquid phase.
19
Q
Why does a fizzy drink fizz when it’s opened?
A
Opening the bottle lowers the pressure above the liquid, creating a partial pressure gradient that causes dissolved CO₂ to escape into the gas phase. On a hot day, higher temperatures further reduce gas solubility, making the drink go flat faster.
20
Q
Define:
partition coefficient
A
Measures the tendency of a solute to dissolve in two different immiscible solvents (phases). It is the ratio of concentrations of a substance in two phases of a mixture of two immiscible solvents.
Written as λ(a,b)
21
Q
Why is a low blood-gas partition coefficient favourable for volatile anaesthetic agents?
A
A low blood-gas partition coefficient means the anaesthetic is less soluble in blood, allowing alveolar partial pressure to rise quickly. This creates a steep gradient for rapid diffusion into the brain, leading to a faster onset of action.
In contrast, high solubility delays this process by slowing the buildup of alveolar partial pressure and reducing the drug’s drive to cross into the brain.
22
Q
Define:
colligative properties
A
Properties of solutions that depend on the NUMBER of molecules of solute in a given volume of solvent rather than the properties of the solute molecules themselves.
23
Q
List some examples of colligative properties.
A
- Vapour pressure
- Osmotic pressure
- Variations in boiling and freezing point
24
Q
What effect does dissolving salt in water have on the boiling and freezing point and why?
A
Dissolving salt in water RAISES the boiling point because solute particles reduce the number of solvent molecules at the surface, hindering evaporation. This means a higher temperature is needed for the vapour pressure to match atmospheric pressure.
It also LOWERS the freezing point because solute particles disrupt the formation of the solid lattice, making it harder for water molecules to freeze.
25
How does a **freezing point change osmometer** work?
Measures osmotic pressure indirectly by detecting changes in the freezing point (colligative property related to solute concentration).
The sample (e.g. urine or plasma) is super-cooled below its expected freezing point while being stirred. As it begins to freeze into a slush-like state (ice-liquid equilibrium), the freezing point is recorded using a temperature probe.
26
How does a **side stream gas analyser** work?
Uses a thin sampling tube to draw a small constant flow of gas (150-200 mL/min) from the breathing circuit to a detector - this is drawn with a slight negative pressure.
A water trap prevents condensation from entering the analyser.
27
What are some **issues** with a side-stream gas analyser?
* Time lag of a few seconds
* Gas mixing in the tube reduces precision
* Vulnerable to occlusion
28
Describe the **difference** in the absorption of infrared radiation by polyatomic gases vs monoatomic gases.
Polyatomic (e.g. CO2, N2O, H2O) absorbs
Monoatomic (e.g. O2, N2) does not
29
State **Beer's law**.
Concentration of a gas is directly proportional to the absorbance of electromagnetic waves.
30
What is the **collision broadening effect**?
Interactions between gas molecules in a mixture cause variations in absorption wavelengths.
This leads to a broadened absorption peak and can shift the peak wavelength.
## Footnote
NOTE: nitrous oxide and CO₂ interact and alter each other's absorbance, so gas analysers must correct for this when measuring ETCO₂ to ensure accuracy.
31
How does an **infrared gas analyser** work?
Generates infrared radiation from a heated wire, which is filtered to a specific wavelength absorbed by the target gas.
The gas passes through a chamber with infrared-permeable windows (e.g. sapphire), and a photodetector measures how much radiation passes through. The amount of absorbed radiation indicates gas concentration (Beer's law).
Some systems include a parallel air-filled control chamber to correct for fluctuations in light source intensity.
32
Why does the plateau of the ETCO2 trace have a **slight upstroke**?
Due to continued diffusion of CO2 across the alveolar membrane during expiration (i.e. alveoli emptying last will contain more CO2 than the ones emptying first).
33
How does a **pulsed-field paramagnetic oxygen analyser** work?
Sampled gas and a reference gas are passed via two separate inlets into the analyser.
A magnetic field is pulsed (~100 Hz) which attracts the paramagnetic oxygen molecules towards the field.
The subsequent change in flow in the sample gas leads to a pressure difference on one side of a double-sided pressure transducer which corresponds to the difference in partial pressure of oxygen between the two gases.
The alternating pressure signal allows for fast, real-time oxygen monitoring, overcoming the slow response time of older paramagnetic analysers.
34
Explain how a **galvanic fuel cell** works.
Detects oxygen by generating an electrical current proportional to the partial pressure of oxygen. Oxygen diffuses into the cell and is reduced at the gold cathode:
O₂ + 4e⁻ + 2H₂O → 4OH⁻
The resulting hydroxide ions migrate through a potassium hydroxide (KOH) electrolyte to the lead anode, where oxidation occurs:
Pb + 2OH⁻ → PbO + H₂O + 2e⁻
This redox reaction creates a flow of electrons from the anode to the cathode, producing a measurable current that reflects the ambient oxygen concentration.
35
Where are **galvanic fuel cells** used and what is one major issue that limits their use?
Used in anaesthetic machines to measure oxygen concentration in supply gas
30 s response time.
Limited lifespan as the anode decreases in size over time.
36
What are the **three types** of electrodes used in arterial blood gas analysis?
* Clark - Oxygen
* Severinghaus - Carbon Dioxide
* Sanz - pH
37
How does the **Clark electrode** work?
Measures pO2 using an electrochemical cell consisting of a platinum cathode and a silver/silver chloride anode, immersed in KCl solution. A small constant voltage (~0.6 V) is applied across the electrodes.
At the cathode, oxygen is reduced:
O₂ + 4e⁻ + 2H₂O → 4OH⁻
At the anode, silver is oxidised:
4Ag + 4Cl⁻ → 4AgCl + 4e⁻
The reduction of oxygen at the cathode consumes electrons, which are supplied by the oxidation of silver at the anode. The resulting electron flow through the external circuit produces a current. This current is directly proportional to the amount of oxygen reduced — and therefore to the partial pressure of oxygen (pO₂).
38
How does the **Sanz electrode** work?
There is a reference electrode made of Ag/AgCl in a KCl solution kept at a fixed voltage.
The measuring electrode is also Ag/AgCl in a pH buffer solution in contact with H+ sensitive glass.
H+ from the sample binds to the hydrated gel layer on the outside of the glass causing an imbalance in H+ between the inside and outside of the glass.
This creates a potential difference that is detected by the measuring electrode and compared to the reference electrode.
39
How does the **Severinghaus electrode** work?
* CO2 from the sample passes through a membrane into a bicarbonate solution.
* It reacts with water to form carbonic acid.
* The H+ is detected by a pH-sensitive glass electrode.
* Ag/AgCl is used as a reference.
40
How does **gas chromatography** work?
Separates components of a gas mixture using a mobile (gas) and stationary (liquid/solid) phase.
Sample is carried through a column by an inert gas (e.g., helium).
Components separate based on how strongly they interact with the stationary phase.
A detector measures retention time (identity) and peak height (concentration).
41
Explain how **mass spectrometry** work?
Gas molecules are ionised by high-speed electrons.
Positive ions are accelerated and deflected by a magnetic field.
Deflection depends on mass-to-charge ratio (m/z).
Detectors measure ion abundance and m/z.
Heavier ions deflect less; lighter ions more.
42
How does **Raman spectroscopy** work?
A beam of EM radiation (photons) is directed at the sample.
Most photons scatter elastically (Rayleigh scattering), with no energy change.
In Raman scattering, a photon excites an electron to a higher energy level.
The electron then relaxes to a different energy level, releasing a photon with a different energy (wavelength).
These energy shifts are unique to molecular structures and are recorded as a Raman spectrum.
43
What is the only **vaporiser-in-circle system** used at present?
Oxford miniature vaporiser
Vapour is added to the gas mixture after it has entered the breathing system.
44
How do **plenum vaporisers** (variable bypass vaporisers) work?
Fresh gas flow splits: some goes through a vaporising chamber, the rest bypasses it.
Positive pressure pushes carrier gas through the chamber, picking up vapour from the volatile agent.
Gases rejoin before reaching the patient.
Splitting ratio controls anaesthetic concentration and can be adjusted.
Vaporiser must maintain the agent's SVP for accurate delivery.
45
How does evaporative cooling **affect** the vapour concentration achieved by a vaporiser?
When a volatile liquid evaporates, high-energy molecules escape, lowering the average energy of the remaining molecules.
This lowers the temperature of the liquid due to latent heat of vaporisation. This affects SVP.
To prevent excessive cooling, a heat sink (material with high specific heat capacity) is used in the vaporiser.
The heat sink absorbs thermal energy to counteract temperature drops, ensuring stable vapour concentration and minimizing fluctuations in the liquid temperature.
46
How do plenum vaporisers **adjust** for changes in temperature?
Anaesthetic output rises with temperature due to increased SVP.
To compensate, variable bypass systems adjust the splitting ratio:
- Higher temperature → more gas bypasses the vaporising chamber.
Thermal compensation mechanisms include:
- Bimetallic strips (most common) that bend with temperature.
- Expanding metal rods or liquid-filled bellows to reduce carrier gas flow at higher temps.
The vaporiser's metal body also helps by conducting heat to stabilise temperature.
47
How does a **dual-circuit vaporiser for desflurane** work?
Desflurane boils at 22.8°C, so it’s stored in the vaporiser at 39°C and 200 kPa to keep it stable.
The vaporiser doesn’t use carrier gas to pick up vapour like others do.
Instead, pure desflurane vapour is injected into the fresh gas stream.
A pressure transducer compares the pressure of fresh gas and vapour.
A pressure correction valve adjusts vapour flow to ensure accurate delivery.
48
Would you need to **change** the vaporiser settings if delivering anaesthetic at altitude?
Partial pressure, not percentage, determines clinical effect.
SVP is constant (temperature-dependent, not pressure-dependent), so partial pressure of vapour remains the same.
However, since atmospheric pressure drops at altitude, the percentage concentration increases.
This means the same partial pressure delivers a higher concentration of agent (e.g., higher % on Everest), but the anaesthetic effect is determined by the partial pressure of the agent.
49
What is a **Bodok seal**?
A neoprene washer placed between the gas cylinder and the cylinder yoke to ensure a gas-tight seal.
50
What is the **pin index system**?
Designed to ensure the correct gas cylinder is attached to the correct inlet on the pressure regulator or anaesthetic machine.
The positions of the holes on the cylinder valve correspond with pins fitted to the yoke attached to the equipment.
The pin positions for each gas are unique.
51
What **features** enable identification of the type of gas within a cylinder?
* Pin index system
* Engraved chemical formula of the gas
* The shoulder of the cylinder should be colour-coded
* An expiry date should be present
52
How **often** does a cylinder need to be internally examined with an endoscope?
Every 5 years
53
What are the **main sizes** of gas cylinder used in clinical practice?
* **A**: smallest
* **CD**: standard for transfer (460 L)
* **E**: used for anaesthetic machines (680 L)
* **J**: biggest (6800 L)
54
Describe the **change in state** of the nitrous oxide with decreases in volume.
At 40°C (above critical temperature of 36.5), nitrous oxide stays a gas regardless of pressure; pressure increases smoothly when compressed.
At 20°C, once pressure reaches 52 bar (its SVP), gas begins to condense into liquid.
Further volume decrease causes more gas to condense without increasing pressure.
After full condensation, any more volume reduction causes a rapid pressure rise, since liquid is incompressible.
55
What is the **filling ratio** of a cylinder and why is it important?
Filling ratio = mass of gas in a cylinder ÷ mass of water that would fill it.
Cylinders are not filled to 100% to avoid dangerous pressure rises with temperature.
Some gas is left above the liquid to absorb expansion safely.
Rising temperature causes liquid to expand, but excess vapour condenses, limiting pressure increase.
In the UK, the maximum filling ratio is 0.75 for safety.
56
Draw a **graph** showing how the pressure of a gas cylinder containing liquid will change as it empties.
The pressure will just show SVP until all the liquid has evaporated.
When empty, it will contain 1 atmosphere (hence, there is no gradient drawing more gas out).
57
What important **storage-related issue** affects Entonox cylinders and how can this be mitigated?
Must be kept above pseudocritical temperature of - 5.5°C (stored at 137 bar).
Below this, lamination occurs (Poynting effect): nitrous oxide liquefies, and the mixture separates into two layers:
Lower layer: liquid nitrous oxide with some dissolved oxygen (~20%).
Upper layer: oxygen-rich gas.
As gas is used, the patient first receives mostly oxygen, then hypoxic nitrous oxide-rich vapour.
Large cylinders use dip-tubes to delay hypoxia by drawing from the liquid layer.
58
What is the **pseudocritical temperature** of a gas mixture?
Temperature below which a gas mixture begins to behave like a single component fluid, meaning it can separate into distinct liquid and gas phases, even though it's a mixture.
## Footnote
NOTE: Nitrous oxide has a much higher boiling point than oxygen.
59
How is **oxygen** produced?
Fractional distillation of liquefied air - air is cooled to -200 degrees and liquefies. It is then heated progressively to the different boiling points of nitrogen, argon and oxygen and the evaporated pure gases are collected.
Chemical oxygen generator (zeolite molecular sieve) absorbs nitrogen and can produce oxygen and is used for home oxygen concentrators.
Electrolysis of water can also be used to generate oxygen (e.g. on submarines).
60
What is the **critical temperature** of oxygen?
-118°C
61
What is **critical pressure**?
The minimum pressure required to liquefy a gas at its critical temperature.
62
What is the **critical pressure** of oxygen?
50 bar
63
What is the **boiling point** of oxygen at atmospheric pressure?
-182.5°C
64
How do **cylinder manifolds** work?
Connect multiple gas cylinders to supply hospitals centrally.
Two banks of cylinders are used; when pressure drops in one, the system automatically switches to the other.
Each bank should provide gas for at least 2 days.
Oxygen cylinders are stored at 137 bar, and pressure-reducing valves drop this to 4 bar for safe pipeline delivery.
65
How do **vacuum-insulated evaporators** work?
Oxygen is stored as a liquid at high pressure (7 bar) and low temperature (-150 to –180 degrees).
The VIE is a thermally insulated vessel.
It has an inner shell of stainless steel and an outer shell of carbon steel.
1 L of liquid oxygen gives 860 litres of gaseous oxygen at STP.
An electrical warmer brings the oxygen to room temperature.
66
At what **pressure** is medical air delivered?
400 kPa for ventilation
700 kPa for pneumatic tools
67
What are the **three methods** of achieving subatmospheric pressure for vacuum suction?
* Mechanical pump
* Centralised piped vacuum source
* Venturi effect driven by gas from cylinders
68
What **negative pressure** must be achieved by a suction system?
A suction system needs to generate a negative pressure of at least 400 mm Hg.
## Footnote
NOTE: Surgical suction needs to achieve negative 500 mm Hg within 10 seconds and remove 25 L/min
69
What is **stoichiometric composition**?
It’s the chemically correct air-fuel ratio for complete combustion — no leftover fuel or oxygen.
Represents the most efficient and often most explosive mixture.
All fuel is fully oxidized using exactly enough oxygen.
## Footnote
Example: For ethanol, the stoichiometric air-fuel ratio is 9:1.
70
What's the **critical temperature** of oxygen?
-118 °C
71
What is the **boiling point** of oxygen at sea level?
-183 °C
72
# Define:
saturated vapour pressure
Pressure exerted by the vapour phase of a substance when in equilibrium with the liquid phase (i.e. molecules entering liquid phase are equal to molecules leaving it).
73
What are the temperature and pressure of a **vacuum-insulated evaporator**?
Temperature: -160 to -180 °C
Pressure: 10 bar
74
What is the boiling point of **nitrogen**?
-196 °C
75
What is the boiling point of **argon**?
-186 °C
76
State the pin index configuration for each of the following gases:
Oxygen
Nitrous Oxide
Air
Nitrogen
Carbon Dioxide
Nitrogen
* Air: 1 + 5
* Oxygen: 2 + 5
* Nitrous Oxide: 3 + 5
* Nitrogen: 1 + 4
* Carbon Dioxide: 1 + 6
77
What's the boiling point of **nitrogen**?
-196 °C
78
What are the **colligative properties** of water?
* Lowers vapour pressure
* Raises boiling point
* Depresses freezing point
* Osmotic pressure
## Footnote
NOTE: colligative properties are physical properties that are dependent on the number of dissolved particles rather than the identity of the solute themselves
79
How is osmotic pressure **calculated**?
Applying the van’t Hoff equation: PV = nRT
Dilute solutions behave in a similar way to ideal gases (osmotic pressure is related to temperature and volume the same way).
80
How is osmotic pressure (osmolality) **measured**?
Freezing point change osmometers.
1 mole of solute added to 1 kg of water depresses freezing point by 1.86 degrees
## Footnote
NOTE: osmolarity (/L) can be calculated by adding the most osmotically active particles together (2 x Na) + glucose + urea
81
Give a **clinical example** of where temperature affects gas solubility.
Fluid warmers can make bubbles escape from the solution (so they need a bubble trap to prevent intravenous injection of bubbles).
82
What's the critical temperature of **carbon dioxide**?
31 °C
83
What are **two methods** of producing oxygen?
* Fractional distillation of air
* Oxygen concentrator (e.g. pressure-swing adsorption)
84
How does **thoracic bioimpedance cardiac monitoring** work?
* 4 electrodes on lateral neck and 4 electrodes on mid-axillary line of chest wall
* Measures resistance to current flowing from outermost electrodes to innermost electrodes
* Fat doesn't conduct electricity, so bioimpedance is related to the water content of the thorax which changes through the cardiac cycle
## Footnote
NOTE: Very sensitive to movement, inaccurate with arrhythmias.
85
What **factors** affect the natural frequency of an invasive blood pressure monitoring system?
NF is proportional to √(r²/clρ)
## Footnote
r = radius of the tubing
c = compliance
l = length
ρ = density of the fluid
86
What is **resonance**?
Every system has a natural frequency which is the frequency at which it will oscillate if disturbed and left alone.
If an external driving frequency is equal to the natural frequency of the system, the system will oscillate with maximal amplitude (resonance).
This distorts the trace.
The components of an arterial line are designed to have a natural frequency of 40 Hz which far exceeds the driving frequency of the heart beat (1-2 Hz).
87
What is **damping**?
Inherent tendency to resist oscillation - loss of amplitude due to energy loss to resistive forces.
88
What is a **Von Recklinghausen oscillotonometer**?
* Double pneumatic cuff
* Proximal cuff occludes the artery
* Distal cuff senses arterial pulsations
* As pressure of proximal cuff is slowly released, the distal cuff senses the oscillations on a pressure gauge
89
How does a **DINAMAP** work?
Device for Indirect Non-Invasive Automatic MAP
Cuff is inflated and slowly deflated - the pressure transducer measures both the pressure and the oscillations
## Footnote
NOTE: For the subsequent BP readings, the cuff will only be inflated to 20-30 mm Hg above the previous SBP readings.
90
What are **some sources of error** in non-invasive blood pressure measurements?
* Cuff size (small over-reads, large under-reads)
* Calcified vessels
* External pressure on the cuff (e.g. leaning on it)
* Extremes of blood pressure
* Arrhythmias
* Obesity
91
Why is **cuff size** important for blood pressure measurements?
Because the pressure measured in the bladder must be effectively transmitted through the arm tissue to occlude the artery.
## Footnote
A cuff that is too small has a smaller contact area, so less of the bladder pressure reaches the artery, requiring higher inflation to achieve occlusion and leading to falsely high readings.
A properly sized cuff distributes pressure efficiently, giving an accurate measurement.
92
# Define:
elastic force
A force that resists deformation.
93
What are the **ways** inspired air can be humidified in an anaesthetised patient?
**Passive:**
* HMEF
* Cold water bath
* Soda lime reaction
**Active:**
* Hot water bath
* Ultrasonic nebuliser
* Gas-driven nebuliser
94
What are the **different ways** in which humidity can be measured?
* Wet and dry bulb hygrometer
* Hair hygrometer
* Dew point (Regnault's) hygrometer
* Electronic hygrometer (humidity-sensitive capacitor or resistor)
95
What are the **methods** used to warm intravenous fluids?
* Dry heat warming systems (e.g. Ranger)
* Magnetic induction heater (e.g. Belmont)
* Counter-current heat exchanger
* Water bath warmer
96
What are the **risks** of using an intravenous fluid warmer?
* Air embolism (need bubble traps/detectors)
* Thermal damage to red cells
* Burns
* Infection
97
What are the **two fixed points** of the **Fahrenheit scale**?
* 32°F = freezing point of water
* 212°F = boiling point of water
98
How can you **classify** methods of measuring temperature?
* Non-electrical
* Electrical
* Infrared
99
What are the **ways** in which you can measure temperature?
**NON-ELECTRICAL**
* Liquid thermometer (mercury, ethanol)
* Bourdon gauge
* Bimetallic strip
* Liquid crystal thermometer
**ELECTRICAL**
* Platinum resistance thermometer
* Thermistor
* Thermocouple
**INFRARED**
* Tympanic membrane thermometer
100
How are **ECG skin electrodes** designed?
Silver metal coated in a thin layer of silver chloride in contact with chloride ion-containing gel.
It is fixed to the skin via an adhesive disc.
Silver/silver chloride is chosen because it is least likely to experience a change in electrical potential due to chloride ions in sweat.
## Footnote
NOTE: Skin should be hairless, clean and dry.
101
What is **signal-to-noise ratio** of an ECG?
Ratio of the magnitude of the biological signal to that of the electrical interference signal.
102
How can the signal-to-noise ratio of an ECG be **improved**?
* Common Mode Rejection
* Filters
* Amplifier
## Footnote
**COMMON MODE REJECTION** (signals that are same in two electrodes are assumed to be noise)
**FILTERS** (used to remove signals above or below a certain frequency)
**AMPLIFIER** (augments the amplitude of the signal)
103
What are the **different types** of filters that are used in an ECG?
* High Pass
* Low Pass
* Band Pass
* Notch Filter
## Footnote
**HIGH PASS** (allows high frequency signals to pass)
**LOW PASS** (allows low frequency signals to pass)
**BAND PASS** (allows frequencies within a certain range to pass)
**NOTCH FILTER** (eliminates a specific band of frequencies such as 48-52 Hz to reduce mains interference)
104
What **sources** of electrical interference may there be in an operating theatre?
**EXTERNAL**
* Capacitive coupling
* Diathermy
* Mobile phones
* Operating table
**INTERNAL**
* Skeletal muscle activity
105
What is the **minimum monitoring** required in recovery?
* Pulse oximeter
* NIBP
* ECG
* Capnography (if LMA in place)
* Temperature
106
How can an MRI machine **interfere** with monitoring signals?
Induction current in wires and electrodes can result in burns (use MR-conditional pulse oximeter and carbon fibre electrodes/wires)
Induction current can lead to interference (use high-impedance, braided leads and carbon fibre electrodes)
107
How many EEG scalp electrodes are there and what is the amplitude of the signal?
16 electrodes
10-50 µV (very small and needs amplification)
## Footnote
Filters block signals that are below 0.5 Hz and above 35 Hz.
108
How can **depth of anaesthesia** be monitored?
* **CLINICAL**: heart rate, blood pressure, sweating, lacrimation
* **MEASURED**: MAC, BIS
* **OTHER**
* Skin conductance (quantification of sweat gland activity which decreases with depth of anaesthesia)
* Frontalis EMG
* Isolated forearm technique
* Lower oesophageal contractility
* Evoked potentials
109
# Define:
electric charge
Physical property of matter that makes it experience a force when placed within an electromagnetic field.
110
What **factors** affect impedance in defibrillation?
* Paddle size (larger means lower impedance)
* Electrolyte gel
* Paddle position (anteroposterior and anterolateral are best)
* Distance between paddles (smaller distance is better)
111
What is **diathermy**?
The heating effect that is seen when high-frequency AC is passed through a small area of tissue.
Can be classified as monopolar or bipolar.
112
What **frequency** of AC is used for surgical diathermy?
0.5-3 MHz
## Footnote
This is because UK mains frequency (50 Hz) has a low threshold for causing VF.
113
When is **bipolar diathermy** preferable?
When current passing through nearby tissues may be harmful (e.g. neurosurgery, ICD).
Good for coagulation (not as good for cutting).
114
What is the **difference** between cutting and coagulation diathermy?
**CUTTING** (yellow pedal)
* Continuous waveform of low voltage
* Generates enough heat to vaporise water contents of cell resulting in cutting
* Bad for coagulation
**COAGULATION** (blue pedal)
* Pulsed waveform of high voltage
* Lower average power which is enough for thermal coagulation but not for cutting
**BLENDED**
* Properties of both
115
What are the **risks** associated with diathermy?
* Electrocution (floating circuit protects against this)
* Poorly applied neutral plate (burns)
* Metal implants can heat up
* Fire
* Interference with monitoring (ECG, EEG)
* ICD/Pacemaker interference (place neutral plate as far from pacemaker as possible or use bipolar)
* Diathermy smoke
116
What are the **two types** of reactance in AC circuits?
1. Inductive
2. Capacitive
## Footnote
**INDUCTIVE** - alternating flow generates a magnetic field around the conductor which opposes further flow of electrons (increases with increasing frequency)
**CAPACITIVE** - decreases with increasing frequency
117
What is the **purpose** of the ferrous core in a transformer?
The ferrous core has high magnetic permeability, guiding and concentrating the magnetic field.
118
How can **magnets** be classified?
* Permanent
* Electromagnet
## Footnote
**PERMANENT**: an object that is magnetised and creates its own persistent magnetic field (e.g. iron).
**ELECTROMAGNET**: passing electric current through a wire produces a magnetic field (can be enhanced by coiling the wire, adding an iron core, increasing the current).
119
What is **microshock**?
It refers to the passage of a very small electric current directly through the heart, typically via an intracardiac or intravascular conductor, which can induce ventricular fibrillation even though the current is too small to be felt by the patient.
120
What are the **two mechanisms** of electrical injury?
* Resistive Coupling
* Capacitive Coupling
## Footnote
**RESISTIVE COUPLING**: Person comes into contact with a source of electricity (e.g. faulty equipment) and an earthed object (e.g. drip stand) so current passes through them.
**CAPACITIVE COUPLING**: Person acts as one plate of a capacitor - AC is induced in your body.
121
What are the **two ways** in which electric equipment in the operating theatre is classified?
**METHOD OF PROTECTION**
* Class 1: earthed
* Class 2: double insulated
* Class 3: SELV
**DEGREE OF PROTECTION**
* Class B: max leakage of < 100 µA
* Class BF: floating circuit (patient circuit not connected to earth)
* Class CF: contact with heart, max leakage < 10 µA
122
What are the **key physical features** of laser light?
* Monochromatic (specific wavelength)
* Coherent (in phase)
* Collimated (parallel beam)
123
What are the **risks** of laser?
* Fire (ignition)
* Operating personnel (eyes)
124
How are the risks of laser **minimised**?
* Safety goggles
* Laser signs on operating room doors
* Blinds and locks on operating room doors
* Matt black surgical instruments to limit reflection
* Designated laser safety officer
125
What are the advantages and disadvantages of **pulse oximetry**?
**ADVANTAGES**: easy to use, non-invasive, continuous
**DISADVANTAGES**: accurate over 70+%, slow response time (10-20 seconds), ineffective when cardiac output is low or arrhythmias
126
How does methaemoglobinaemia **affect** a pulse oximeter?
Roughly equal absorption of 660 and 940 nM meaning that it tends to give a fixed saturation reading of 85%.
127
What **absorption wavelengths** are tested by a Haemocue?
570 nM
880 nM
## Footnote
NOTE: It is measuring azide-methaemoglobin.
128
What is the **difference** between an active and passive transducer?
**ACTIVE**: generate electric CURRENT or VOLTAGE directly in response to stimulation (thermocouple, piezoelectric transducer).
**PASSIVE**: requires external power source and involves change in resistance/inductance/capacitance (e.g. thermistor).
129
What is the **normal frequency range** used by medical ultrasound?
2.5-15 MHz
130
Describe the **structure** of an ultrasound probe.
Piezoelectric crystals oscillate at the frequency of the current applied thereby generating ultrasound waves.
Backing material ensures sound energy only goes forward.
Acoustic lens focuses the ultrasound beam.
131
What are the **different modes** used on ultrasound?
* A
* B
* M
* Doppler
## Footnote
**A**: simplest mode, plots amplitude against depth as a graph
**B**: 'brightness' - 2D image
**M**: rapid sequence of B mode images to assess a moving structure
**Doppler**: assess whether moving towards or away from the probe
132
What **causes** signal attenuation of ultrasound?
* Absorption (by tissues)
* Reflection and scattering
* Refraction (continues forward at deflected angle)
* Divergence (passing through obstacle spreads it out)
133
What are the **main mechanisms** of operation of ventilators?
* Minute-volume dividers (Manley MP3)
* Bag squeezer (most common)
* Intermittent blowers (mostly in ITU, oxylog)
134
What are the **main methods** of ventilation cycling?
* Volume cycled
* Time cycled
* Pressure cycled
135
How are **breathing systems** classified?
* Open (cupped hand)
* Semi-Open (Mapleson)
* Semi-Closed (Circle)
* Closed (Circle with APL Closed)
136
What are the **features** of an ideal breathing system?
* Suitable for a wide variety of patients
* Efficient for spontaneous and controlled ventilation
* Low dead space
* Efficient removal of CO2
* Efficient scavenging
* Cheap
* Lightweight
* Disposable
137
What are the advantages and disadvantages of a **circle system**?
**ADVANTAGES**: low-flow anaesthesia, preserves heat and moisture, wide range of patients (down to 10 kg), allows scavenging.
**DISADVANTAGES**: multiple points of disconnection, valves increase resistance to flow, gas mixture delivered takes time to change (3-5 L internal volume).
138
Outline the **soda lime reaction**.
H₂O + CO₂ → H₂CO₃
2NaOH + H₂CO₃ → Na₂CO₃ + 2H₂O
Na₂CO₃ + Ca(OH)₂ → 2NaOH + CaCO₃
**OVERALL**: CO₂ + Ca(OH)₂ → CaCO₃ + H₂O
139
What are the **constituents** of soda lime?
* Calcium hydroxide (> 80%)
* Sodium hydroxide (4%)
* Water (15%)
* Indicator dye
## Footnote
NOTE: pH is 13.5
140
What are the **two most commonly used indicator dyes** in soda lime?
* Ethyl Violet --> purple when exhausted
* Phenolphthalein --> white when exhausted
141
What are the **disadvantages** of soda lime?
* Decomposition of sevoflurane to compound A (nephrotoxic in rats).
* Dry lime can produce carbon monoxide (with desflurane, isoflurane and enflurane).
142
What are **some alternatives** to soda lime?
* Baralyme (barium hydroxide, no longer used)
* Amsorb Plus (calcium hydroxide and calcium chloride, more expensive)
143
What is **channeling** in the context of soda lime?
Preferential passage of gases through soda lime canister via low resistance pathways.
The issue is that the soda lime located near the channel is exhausted quickly, resulting in rebreathing.
More spherical and uniform granules prevents channeling.
144
What is the **reservoir bag** made of?
Antistatic latex-free material.
Standard size is 2 L for adults, 1 or 0.5 L for paediatrics.
145
How is a fibreoptic endoscope **decontaminated**?
* Clean external surface manually
* Suction channel - enzymatic detergent then sterile water
* Disinfection with liquid immersion of peracetic acid
* Dried and stored
146
What are the **four mechanisms** by which filters work?
* Direct interception
* Brownian motion
* Inertial impaction
* Electrostatic deposition
147
What is the **pore size** of a filter needle?
5 µm
Filters out glass particles
148
What are the **three types** of radioactive decay?
* Alpha
* Beta
* Gamma
## Footnote
**ALPHA**: emission of helium nucleus, heavy and can only travel a few cm, cannot penetrate skin
**BETA**: emission of electron from nucleus (from transformation of neutron to proton), penetrates matter more easily (e.g. iodine-131)
**GAMMA**: high-energy photon, zero mass, highly penetrating, e.g. PET scan
149
How are X-rays **generated**?
Current passes through tungsten cathode which releases electrons.
Electrons are accelerated towards anode by 100 kV field.
Electrons strike tungsten alloy anode and release X-rays.
150
How are staff and patients **protected** from X-rays?
* Clinically justifying exposure
* Minimising dose of radiation used
* Considering pregnancy and child-bearing potential
* Shielded X-ray rooms
* Lead aprons and thyroid shields
151
What is a **Sievert**?
1 Sievert = 5.5% risk of developing cancer as a result of exposure
CXR is 20 µSv
CT chest is 8 mSv
## Footnote
NOTE: Gray is another unit of radiation dosage - equal to 1 J of ionising radiation absorbed by 1 kg of matter.
152
Describe the **physics** underpinning MRI.
* Hydrogen atoms are abundant in the body
* They possess spin
* When surrounded by a strong magnetic field (1-2 Tesla), the hydrogen atoms align with the magnetic field
* A radiofrequency pulse will invert its alignment
* As the nuclei realign, the net magnetisation vector induces a current in the receiver coil
* The surrounding environment affects the signal produced
153
How is equipment classified based on **MRI compatibility**?
* MRI Safe
* MRI Conditional (based on static field strength, rate of change of magnetic field)
* MRI Unsafe
154
What are the **components** of vacuum suction?
* Source of vacuum (e.g. central)
* Vacuum control box (switch, controller valve, manometer, filter)
* Reservoir canister with disposable lining
* Tubing
## Footnote
NOTE: Should generate 40-50 kPa absolute pressure and 20 L/min flow.
155
What **pressure** is achieved by a central vacuum plant?
**At plant**: 40 kPa
**At wall inlet**: 60 kPa (flow rate of at least 40 L/min)
## Footnote
NOTE: The vacuum is generated by multiple electrically-driven rotary vane pumps.
156
How do **portable suction devices** work?
Use the Venturi effect - pass pressurised gas through a narrowing and create a low pressure area which is connected to suction tubing.
157
Describe how volume, flow and pressure changes in **volume control ventilation**.
Set flow until the volume is achieved.
158
Describe how volume, flow and pressure changes in **pressure control ventilation**.
Set pressure for a given time.
Flow decreases exponentially as the lungs fill.
159
What is the boiling point and critical temperature of **carbon dioxide**?
**Boiling Point**: -79 °C
**Critical Temperature**: 31 °C
160
What are the **two main mechanisms** of measuring intracranial pressure?
* External Ventricular Drain
* Bolt (Pressure Transducer)
## Footnote
**EXTERNAL VENTRICULAR DRAIN**: gold standard for measuring ICP and can drain excess CSF.
**BOLT (PRESSURE TRANSDUCER)**: continuous measurement, measure localised pressure (not representative of global ICP but useful for trends), can drift.
NOTE: Average intracranial volume is 1700 mL = 1400 mL brain + 150 mL CSF + 150 mL blood.
161
State **three mechanisms** of cerebral blood flow measurement.
* Transcranial Doppler
* Jugular Bulb Catheterisation
* fMRI / PET
## Footnote
**TRANSCRANIAL DOPPLER**: most common, assesses flow in MCA
**JUGULAR BULB CATHETERISATION**: insert catheter into jugular bulb, can sample blood for pO2, Hb O2 saturation and lactate (thereby assessing adequacy of CBF)
162
How are flowmeters affected at **altitude**?
Variable-orifice flowmeters are calibrated at sea level.
They under-read at high altitude due to a reduction in gas density.
## Footnote
NOTE: The number of molecules and not the volume of gas matters clinically so flowmeters can be used as per usual.
163
How do you set the current on a **pacing defibrillator**?
* Set pacemaker to demand mode (only delivers current if no intrinsic beat).
* Set rate to 60 beats/min.
* Increase current until electrical capture is achieved.
* Set current threshold at 5-10 mA above pacing threshold.
164
How does a pulse oximeter account for **background noise**?
* Time division multiplexing.
* The lights will turn on in turn (red and infrared) followed by both lights being turned off (to account for ambient light).
* This cycle is repeated 30 times per second.
165
State **Stefan-Boltzmann law**.
The total energy radiated per unit area of a blackbody is proportional to the fourth power of its absolute temperature.
166
What is **Raman spectroscopy**?
When radiation passes through a gas, most is Rayleigh-scattered (no wavelength change), while a small fraction undergoes Raman scattering (wavelength shift) specific to the molecule’s chemical bonds.
This scattered light is then filtered for the target wavelength before reaching a photodetector.
167
What is the **point of the float** in a suction reservoir canister?
When the reservoir fills up, the float will make contact with the top of the canister and occlude the outlet.
This prevents suctioned liquid from passing into the pump.
168
How does ICU endotracheal suction apparatus **differ** from the soft suction catheters used in theatres?
* Allows continuous mechanical ventilation.
* No loss of PEEP.
* Reduced risk of airway contamination.
169
State the **equation** for Reynolds number.
Re = velocity x density x diameter/viscosity
< 2000 = laminar
> 4000 = turbulent
170
What are **some safety features** of a plenum vaporiser?
* Wicks and Baffles (maximises surface area and time for saturation)
* Heat sink (minimise temperature change in liquid)
* Temperature compensation (bimetallic strip or bellows alters splitting ratio)
* Anti-spill mechanism
* Selectatec system
* Colour-coded
* Unique filling port
171
Draw a **Tec 6 desflurane vaporiser** and explain how it works.
Dual-circuit, gas-vapour injection vaporiser designed for desflurane.
Has a sealed, heated vaporising chamber (39 degrees at 2 atmospheres).
It injects precise amounts of desflurane into the FGF downstream.
A differential pressure transducer senses FGF pressure and two pressure regulating resistors adjust internal desflurane vapour pressure to match FGF pressure (enables reliable injection of desflurane).
The second resistor sets the output concentration.
172
Why is pipeline gas **dry**?
Prevents condensation and corrosion.
173
Describe how the **galvanic fuel cell** works.
COMPONENTS: gold cathode, lead anode, KOH solution, ammeter
Cathode: O2 + 4e- + 2H2O --> 4OH-
Anode: Pb + 2OH- --> PbO + H2O + 2e-
Higher pO2 means greater current.
174
What are the advantages and disadvantages of a **galvanic fuel cell**?
**ADVANTAGES**: compact, no power supply
**DISADVANTAGES**: finite lifetime, slow response (20 s), affected by temperature
175
How does a **Clark electrode** work?
**COMPONENTS**: platinum cathode, Ag/AgCl anode, KCl solution, 0.6 V battery, ammeter
Cathode: O2 + 4e- + 2H2O --> 4OH-
Anode: Ag + Cl- --> AgCl + e-
Higher pO2 means more electrons consumed at the cathode and generated at the anode --> increased current
176
What are the advantages and disadvantages of the **Clark electrode**?
**ADVANTAGES**: reliable, small blood sample required
**DISADVANTAGES**: 30 s response time, needs electricity, plastic membrane can be damaged, regular calibration required
177
How does a **paramagnetic oxygen analyser** work?
O2 has unpaired electrons making it weakly attracted to a magnetic field (paramagnetic).
2 nitrogen-filled glass spheres linked by a bar are suspended in a chamber.
Magnets on either side create a non-uniform magnetic field.
O2 is attracted towards the magnetic field which displaces the glass spheres against the torque of the wire.
Degree of rotation is proportional to the amount of oxygen (light reflected by mirror onto scale).
178
How does a **pulsed-field paramagnetic analyser** work?
COMPONENTS: separate test and reference gas limbs, pulsed field (100 Hz), differential pressure transducer.
When the magnetic field is on, O2 is attracted to the magnetic field and this increase in velocity causes a dip in pressure in the test gas limb.
This is detected by the differential pressure transducer and calibrated against known concentrations of O2.
179
What are the advantages and disadvantages of a **pulsed-field paramagnetic oxygen analyser**?
**ADVANTAGES**: accurate, rapid, breath-by-breath, robust with few moving parts
**DISADVANTAGES**: interference from water vapour and nitrous oxide
180
How does a **mass spectrometer** work?
* Vaporised gas sample is ionised by bombardment with electrons.
* Charged molecules are accelerated through a magnetic field.
* Deflection depends on mass-to-charge ratio.
* Detector identifies and quantifies ions in the gas sample.
## Footnote
NOTE: Rapid and accurate but very expensive and bulky.
181
What is **transcutaneous oxygen** measurement?
Essentially a Clark electrode attached to the skin (provides continuous pO2 value).
## Footnote
Occasionally used in NICU.
182
What is an **isotherm**?
Line of constant temperature that illustrate phase changes of a particular substance with pressure and volume.
183
# Define:
kelvin
SI unit of temperature with 0 K being absolute zero.
Historically defined as 1/273.16 of the triple point of water.
184
What is **moisture deficit** with regards to inspired gases?
Moisture deficit = 44 g/m^3 − absolute humidity of inspired air
E.g. room air at 21 °C and 50% relative humidity has an absolute humidity ~9 g/m^3
Moisture deficit = 44 – 9 = 35 g/m^3
This means the respiratory tract must add 35 g of water per metre cubed of inspired air to reach fully saturated conditions.
## Footnote
NOTE: g/m^3 and mg/L are the same value.
185
How does the **pH electrode** work?
COMPONENTS: Ag/AgCl measuring and reference electrode, HCl buffer around measuring electrode, KCl buffer around reference electrode.
pH sensitive glass in contact with blood sample.
Difference in H+ activity across the membrane is detected as a potential difference by the voltmeter.
186
How does temperature **affect** blood pH?
At lower temperatures, the solubility of CO2 and O2 is increased meaning that the blood pH is increased.
This means that when a blood sample from a hypothermic patient is warmed in the gas machine, the measured pCO2 will be higher and the pH will be lower.
187
How much does pH and PaCO2 **change** for every degree drop below 37 degrees?
pH 0.015
pCO2 0.27 kPa
188
What **FiO2** can be achieved with an Ambu bag?
No Reservoir Bag: 40-60%
Reservoir Bag: 80-90%
189
Describe how **Haldane's apparatus** for measuring gas composition works.
A known volume of mixed gas is introduced into the apparatus.
The gas is passed sequentially through absorption chambers containing:
1. KOH (potassium hydroxide) → absorbs CO₂
2. Alkaline pyrogallol → absorbs O₂
The remaining gas (mostly N₂) is measured by difference.
The change in volume after each absorption step gives the percentage of each gas.
190
What are the **benefits** of two-point calibration of an arterial line?
Corrects both offset error (by zeroing it) and gain error (by testing against a second, known pressure value).
191
# Define:
thermostat
A device that senses temperature and actively maintains it at a set point by controlling a system (heating or cooling).
## Footnote
E.g. bimetallic strip, expanding bellows
192
What is a **transistor**?
Semiconductor device that amplifies or switches electrical signals.
It allows a small input to control a larger current flow (useful for things like triggering alarms).
193
What is the **difference** between operational amplifiers and differential amplifiers?
**OPERATIONAL**: high-gain semiconductor that takes in two inputs and can amplify, integrate and compare.
**DIFFERENTIAL**: designed to amplify the voltage difference between two inputs whilst rejecting common signals.
## Footnote
**EXAMPLE**: in an ECG, a differential amplifier amplifies the voltage difference between electrodes whilst rejecting noise (often using an operational amplifier internally)
194
How is **laser light** produced?
Energy is applied to atoms of the **lasing medium** which moves it from the ground state to the excited state.
Electrons then spontaneously fall back to their resting orbits which releases energy.
**Mirrors** will reflect photons back into the lasing medium, triggering more photons to be released.
One mirror has a small hole to allow laser light to pass through.
195
How is a **Clark electrode** calibrated?
2-point calibration with two samples of gas of known concentration (21% and 100% oxygen).
196
What electrodes and solutions are used in the **Severinghaus electrode**?
* **Measuring**: 0.1 M HCl buffer (known H⁺ concentration), Ag/AgCl electrode, sodium bicarbonate buffer (distal side of glass membrane)
* **Reference**: KCl solution
197
What **gas flow** is required to prevent rebreathing through a Bain system in spontaneous vs mechanical ventilation?
Spontaneous: 2-3 times
Controlled: 1-1.5 times
198
How would you **test** a Bain circuit prior to patient connection?
2-bag test
Occlude inner tube with plunger of 2 mL syringe and rotameter of flow-meter should dip (increased pressure in inner tube).
PETHICK Test: close APL, press O2 flush, reservoir bag empties due to Venturi effect (entrainment of gas from expiratory limb into high velocity inspiratory limb).
199
What are the advantages and disadvantages of a **Mapleson F circuit**?
**ADVANTAGES**
* Low resistance to breathing
* PEEP can be adjusted
* Efficient for controlled ventilation (FGF 1-2 times)
**DISADVANTAGES**
* No scavenging
* Inefficient for spontaneous ventilation (FGF 2-2.5 times)
200
What are the advantages and disadvantages of a **Mapleson C circuit**?
**ADVANTAGES**
* Easy to assemble
* Portable
* Can apply PEEP
**DISADVANTAGES**
* Rebreathing occurs even at high flows
* Inefficient for both spontaneous and controlled ventilation
201
Describe how a **TEG** works.
* Sample of blood in cup
* Cup rotated slowly and starts to coagulate
* Torsion pin is lowered into blood sample and clot forms
* Torsion of wire is measured and plotted as deflection on graph
202
What do the **parameters** on the TEG mean?
* **R-Time**: time for clot formation (related to clotting factors)
* **K-Time**: time to reach certain firmness (20 mm) - related to fibrinogen + platelets
* **Alpha-Angle**: rate of clot formation (related to fibrinogen and platelets)
* **MA**: max clot strength (related to fibrinogen and platelets)
* **CL30**: activity of fibrinolytic pathway
203
What are the **benefits** of TEG/ROTEM?
* Point-of-care
* Tests whole blood
* Provides information on coagulation and fibrinolysis
* Assessed platelet function
204
What is the **frequency** of surgical diathermy?
0.5-3 MHz
## Footnote
NOTE: This range does not depolarise nerves or muscles.
205
What are **some hazards** associated with surgical diathermy?
* Electrocution (isolating transformer prevents this)
* Burns at neutral plate
* Risk of fire
* Interference with monitoring
* Interference with ICDs
* Diathermy smoke (hazard to staff)
206
How can the risk of diathermy to a patient with a pacemaker be **reduced**?
* Switch to fixed pacing mode.
* Use bipolar instead of monopolar.
* Place neutral plate as far from pacemaker as possible.
207
What is the pore size of a **blood-giving set filter**?
170-200 µm
## Footnote
NOTE: This is to filter blood clots and other aggregates.
208
What is the pore size of a **filter needle**?
5 µm
Used to filter glass particles from open ampoules
209
What are the electrodes and solution in a **galvanic fuel cell**?
* CATHODE: Gold
* ANODE: Lead
* SOLUTION: Potassium Hydroxide (KOH)
210
What are **three safety features** of a Schrader valve?
* Size of valve is specific to each gas.
* Valve is named and colour-coded.
* Internal valve so that unplugging hose closes supply.
211
What are **some safety features** of the gas pipeline system within a hospital?
* Low pressure alarms detecting supply failure
* Isolating valves at strategic points
* Made of copper alloy (prevents degradation of gases and is bacteriostatic)
* Regular testing
212
What are the **different components** of a cylinder manifold?
* non-return valve
* pressure-reducing valve
* shuttle mechanism
* 137 bar
* 4 bar
## Footnote
NOTE: The cylinders are size J.
213
What are two advantages and disadvantages of **vacuum-insulated evaporators**?
**ADVANTAGES**
* Cheaper to deliver and store oxygen
* Less storage space required
**DISADVANTAGES**
* Risk of fires and explosions
* Low usage can lead to wastage (blow-off valve)
214
What is the **normal range** for relative humidity in the theatre environment?
40-60% at 20 °C
215
Name the **different parts** of the endotracheal tube.
* Bevel
* Murphy's Eye
* Cuff
* Vocal Cord Guide
* Internal Diameter
* 15 mm Adapter
* Spring-Loaded One-Way Valve
* Pilot Balloon
216
What **type** of endotracheal tube is this?
North-Facing RAE
217
What **type** of endotracheal tube is this?
Montandon tube
| (laryngectomy)
218
What **features** prevent a bobbin in a rotameter from sticking and ensures that it is always visible?
* It stops at top and bottom of tube.
* Anti-static coating within tapered tube.
* Grooves to make the bobbin rotate.
219
What **frequency range** is used by medical ultrasound?
2--15 MHz
220
What are the **main causes** of ultrasound signal attenuation?
* **Absorption**: energy converted into heat
* **Reflection**: some energy bounces back at tissue interfaces
* **Scattering**: energy dispersed in multiple directions
* **Divergence**: acoustic energy spreads out after passing through an obstacle
221
What are the **three types** of vaporiser?
* Draw-over
* Plenum
* Vapour-injection (Tec 6)
222
How do plenum vaporisers ensure that the chamber is **fully saturated**?
* Wicks (increase surface area)
* Baffles (slow down gas)
* Heat reservoir
* Temperature compensation
223
What **safety features** prevent a vaporiser from being filled with the wrong gas?
* Colour-coding
* Geometric-specific filling device
224
What is the **pumping effect** with regards to vaporisers?
Intermittent back pressure due to positive pressure ventilation pushes gas that contains anaesthetic into the bypass stream.
When pressure is relieved, this combines with vaporiser output producing a gas with a higher than desired concentration of agent.
Prevented by a long, high resistance outlet of the plenum vaporiser and a one-way valve.
225
What is the purpose of the **selectatec system**?
Prevents more than one vaporiser from being switched on.
226
What is **synchronised intermittent mandatory ventilation**?
Ventilator delivers pre-set volume or pressure at pre-set rate.
If there is negative pressure due to patient effort, the ventilator supports this breath with some pressure.
227
Aside from the end-tidal CO2 value, what other **clinical information** can be ascertained from a capnography trace?
* Respiratory rate
* Cardiac output
* Tracheal intubation
* Airway obstruction (e.g. bronchospasm)
* Circuit leak
* Exhausted soda lime
* Wearing off of neuromuscular blockade
228
Under what **conditions** might a pulse oximeter be inaccurate?
* Low cardiac output
* Peripheral vasoconstriction
* Arrhythmias
* Patient movement
* Venous pulsation (e.g. tricuspid regurgitation)
* Presence of other haemoglobin (e.g. MetHb)
229
How does a **tympanic thermometer** work?
All objects above 0 kelvin emit electromagnetic radiation.
Wavelength of the electromagnetic radiation depends on the temperature.
At 37 degrees, the emitted radiation is in the infrared light range.
230
# Define:
decontamination
Process of removal, inactivation or destruction of pathogens on the surface of equipment.
Consists of cleaning, disinfection and sterilisation.
231
What are the **two main approaches** to disinfection?
* Thermal
* Chemical
## Footnote
**THERMAL** (e.g. pasteurisation, autoclave, ionising radiation)
**CHEMICAL** (e.g. hydrogen peroxide, ethylene oxide)
232
How does an **autoclave** work?
Sterilises using steam under pressure
121 degrees at 2 atmospheres for 20 mins
OR
134 degrees at 3 atmospheres for 4 mins
Primary FRCA
flashcards
Decks in class (17)
# Cards
-
Anatomy for Anaesthesia223
-
Physiology: Respiratory303
-
Physiology: Cardiovascular179
-
Physiology: Renal, Hepatic & GI63
-
Physiology: Neuro, Endo, & Haem237
-
Pharmacokinetics and Pharmacodynamics213
-
Pharmacology: Inhalational & Intravenous Agents232
-
Pharmacology: Analgesics & Muscle Relaxants160
-
Pharmacology: Emergency & Miscellaneous Drugs251
-
Part 1: Physics & Equipment242
-
Part 2: Physics & Equipment227
-
Part 3: Physics & Equipment232
-
Part 4: Physics & Equipment217
-
Statistics & Evidence-Based Practice36
-
Part 1: Applied Clinical Anaesthesia165
-
Part 2: Applied Clinical Anaesthesia169
-
Part 3: Applied Clinical Anaesthesia157
